Follow-up apparatus



Feb. 11, 1947. BURNS FOLLOW-UP APPARATUS Fi led Oct. 1, 1942 IN VENT OR. Fen/w: flan/440 flue/v5. BY m a /W Patented Feb. 11, 1947 FOLLOW-UP APPARATUS Frank Donald Burns, Long Beach, 11111., assignor to The Hays Corporation, Michigan City, Ind., a corporation of Indiana Application October 1, 1942, Serial No. 460,391

6 Claims.

This invention relates to a follow-up apparatus.

It is frequently desirable, in controlling a, process, such as a combustion process, or in indicating or recording a variable condition in a process, to actuate a follow-up member, such as a controller, indicator or recorder, in response to variations in the process or condition. The actuation of the follow-up member requires a certain amount of power or torque depending upon the character thereof. In some instances it is possible to connect the follow-up member for actuation by a primary shiftable member, such as a metering device responsive to variations in the process or condition, without introducing any substantial error or lag in the operation of the follow-up member and metering device. However, many applications exist where the primary shiftable means or the means or condition to which it responds is of such character that any direct driving or actuating connection of the follow-up member with the primary shiftable member is impractical because the load imposed on the primary member by the follow-up unit is excessive, and introduces lag or error in the operation of the primary member. Sometimes this efiect can be overcome by using a primary shiftable member, such as a metering device, designed to be properly responsive to the variable and also to have ample power to operate a follow-u member,but this may be objectionable from the standpoint of high cost, excessive space consumption, or for other reasons.

Therefore, it is the primary object of this invention to provide a, power booster adapted to be interposed between a primary shiftable member and a follow-up member which responds instantly, accurately and proportionally to all movements or operations of the primary shiftable member, and which consumes very little torque or power so that error or lag in the operation of the primary member is avoided.

A further object is to provide a device of this character wherein mechanical lag or dead zone is substantially completely avoided.

A further object is to provide a device of this character which is substantially infinitely sensitive to the operation of a primary shiftable memher.

A further object is to provide a device of this character which may be used with a primary shiftable member which develops only a small amount of torque or power.

A further object is to provide a device of this character which is simple in construction, and inexpensive to manufactur and operate.

2 A further object is to provide a device of this character having a reversing motor, a switch con- .trolling the direction of rotation of said motor and including a pair of pivoted parts, and means operated by said motor for positioning one of said switch parts, the other switch part being shiftable by a primary shiftable member.

Other objects will be apparent from the description and appended claims.

In the drawing the single figure is a diagrammatic view illustrating the application of the invention in a gas flow meter.

Briefly stated, this invention utilizes a reversible electric motor, preferably of the three lead type, as the driving means for a follow-up member. This motor has a crank type driving connection with a follow-up contact arm juxtaposed to a contact arm shiftable by a primary shiftable member. The contact arms constitute a switch in the electrical circuit for the motor. The motor is so connected with said circuit that it rotates in a direction to shift the follow-up contact arm in the direction of the contact arm controlled by the primary member when the contacts on said arms are spaced apart, and rotates in a direction to separate th contact arms when the contacts on said arms are in engagement or circuit making relation.

Referrin to the drawing, wherein the invention is illustrated as applied to a gas flow meter, the number 10 designates a conduit or passage in which is interposed a transverse plate I I provided with an orifice I2. Conduit I 0 is tapped at opposite sides of orifice plate II for communication of a high pressure tube I 3 and a low pressure tube M. The mounting of the orifice plate and the connection and positioning of the high and low pressure tubes or lines relative thereto is well understood in the art.

The tubes or lines I3 and I4 extend to any suitable metering device I5 responsive to differential pressure. The metering device selected for illustration is of the slack leather diaphragm type and comprises a two part housing [6 formed of two substantially complementary parts secured together and clamping the margin of a slack leather diaphragm ll therebetween. Diaphragm l1 separates the interior of the housing into a high pressure chamber l8 with which tube l3 communicates and a low pressure chamber IS with which tube l4 communicates. A pair of thin metal plates 20 bear against opposite faces of diaphragm I! and are suitably interconnected. Plates 20 mount one end of a rigid rod 2| extending perpendicularly thereto at the center of the .housing. One of the parts of housing I6 is provided with a small opening 22 therein at the center thereof, and a slack leather diaphragm 23 is marginally secured to said housing to span and seal said opening. Rod 2| projects through and has a sealed connection with diaphragm 22,

An arm 24 is fixedly carried by and projects from the side of housing l6 in-whi-ch opening 22 is formed. A lever 25 is pivoted to arm 24 at 26, said arm and lever preferably being arranged in mutually intersecting or crossed relation. Lever 23 is also pivotally connected to the outer end of rod 2| at 21 in spaced relation to pivot 26. Suitable means are provided for limiting the pivotal movement of lever 25. This means ishere illustrated as a stop member 28 carried by housing It and having shoulders or projections 29 positioned on opposite sides of lever 25 and spaced apart a distance greater than the width of said lever. The lever 25 has a suitable loading sprin 30 connected thereto and adapted to exert tension in opposition to the pressure exerted upon the diaphragm at the high pressure side thereof.-

A second or follow-up lever 3| is pivoted at 32 on the outer end of arm 24 in spaced relation to pivot 26. Lever 3| extends alongside lever 25, and its length is substantially equal to the spacing of the free end of lever 25 from its pivot 26. A link 33 is pivoted at one end at 34 to lever 3| adjacent the free end of said lever. The opposite end of link 33 is pivoted at 35 to a cam 33. Cam 36 is mounted upon the drive shaft 31 of an electric motor 38. Pivot 35 is spaced from shaft 31. Motor 38 is reversible, and as here shown is a three lead condenser type motor.

A pair of leads 39' and 40 are connected with any suitable source of power. Lead 39 is connected to the center tap of motor 38. Lead 40 as herein shown has a resistance 4| interposed thereinand is connected with another tap of motor 38. A flexible lead 42 branches from lead 40 ahead of resistance 4| and is connected with a contact 43 mounted on the inner face of follow-up lever 3| at the free end thereof. A contact 44 is mounted on the free end of lever 25 facing contact 43 and adapted to be engaged thereby, and a flexible lead 45 is connected with contact 44 and extends to the tap of motor 38 opposite that to which lead 40 is'connected.

The follow-up members of theflow meter here illustrated are assumed to be a chart pen or indicating pointer 45 which may be pivoted at 41 upon the instrument housing (not shown) to swing in a path in a plane perpendicular to the axis of motor shaft 31, and a suitable integrator (not shown). As here illustrated, one end of a link 48 serving to operate said integrator is pivoted to member 46 at 49. Member 46 alsomounts a roller 59 which bears against the edge f cam 33. It will be understoodthat a suitable housing or casing will be provided for encasing the parts of the instrument above described, together with means for mounting and driving a recorder chart or for mounting a dial or face plate if the instrument is an indicator. Member 46 is preferahly urged in the direction of cam 36 by a spring 52 connected with the instrument housing.

The device operates as follows: When the switch, i. e., contacts 43, 44, is open, the motor operates in a clockwise direction, being energize'd by the following circuit: line 40, resistance 4|, motor 38, and line 39. This operation of" the motor servesto engage the switch contacts 43 44. When the switch contacts engage, themot'or'supply comes principally through line 40; line 42-,

contacts 43 and 44, line 45, motor 38 to line 39, causing the motor to operate in a counterclockwise direction to re-open contacts 43 and 44. Hence the motor constantly operates in reverse directions to alternately engage and disengage contacts 43 and 44, and the action may be described as a hunting action. Inasmuch as only a slight bodily movement of link 33' is required to eiiect this alternate engagement and disengagement oi the contacts, the hunting action of the motor does not produce any substantial movement of arm 46, and hence for a given constant condition, i. e., one where diaphragm remains substantially stationary, no material deviation is recorded upon chart 5| due to the hunting action.

When a change occurs in the process to which the metering device I5 is responsive, such as a. change in differential pressure occasioned by a change in the rate of fluid flow in passage H], the diaphragm shifts proportionally to said change or variation. The rod 2| is shifted endwise by the diaphragm to pivot lever 25 about its pivot 26. This results in the assumption. of a new position by the contact 44. If the new position is in the direction of contact 43, the counterclockwise movement of the motor necessary to separate contacts 43 and 44 will be greater than that occurring durin normal hunting operation of the motor, with the result that the rotation of cam 36 will be sufficient toswing arm 46 relative to the chart to designate the new condition measured by the metering device. The chart 5| will be properly calibrated to give an accurate reading of the measured condition. If the condition being measured results in a movement of the diaphragm to shift contact 44 away from contact 43, the clockwise operation of the motor necessary to effect engagement of contact 43 with contact 44 will be increased, and will cause a corresponding deflection of arm 46 relative to the chart 5|.

The stop 28 is provided to maintain the device on the proper working portion of the cam. Thus, said stop prevents displacement of lever 25 Man extent wherein the roller runs over the large diameter cam portion onto the flat substantially radial portion of the cam edge. Limit switches or other limiting devices may be used in place of stop 29.

It will be observed that the primary shiftable member, i. e., metering device diaphragm, is only required to pivot the lever 25. All other parts are power driven by motor 38. primary shiftable member has'no substantial" load or torque applied thereto, and is free to respond quickly and accurately to all variations in the process with which it is connected. This insures effective elimination of mechanical lag and dead zones in the device. The device is infinitely sensitive since it operates continuously in make and break cycles and hence will instantaneously follow-up variations in the primary shiftable member as the same occur. The simplicity of the device-makes it reliable, easy 'tooperate, and permits its manufacture at low cost. Also, the elimination of application of torque to the'primary shiftable member, 1. e., the diaphragm, except for loading purposes, permits the use of a comparatively small diaphragm in the metering device. Ample power for any purpose to which the device may be put, 1. e., indicating, recording, integrating, or power application, is obtained by selecting a motor having the necessary powerin addition to required response characteristics.

I'claim:

1. A folloW-upapparatus comprising aprimary Consequently, the

shiftable member, a rigid pivoted lever shiftable by said primary member, a second rigid pivoted lever adjacent to said first lever, a contact mounted on the free end of each lever, said contacts being adapted for engagement, a reversible electric motor, a cam driven by said motor, a direct driving connection between said motor and said second lever, an electrical circuit independent of said contacts for energizing said motor for rotation in a direction to elfect engagement of said contacts and including a resistanc directional circuit for energizing said motor ror rotation in the opposite direction, said contacts forming a switch in said directional circuit whereby said motor is energized under control of one or the other of said circuits at all times, and a pivoted follow-up member engaging the periphcry of and actuated by said cam.

2. A follow-up apparatus comprising a. primary shiftable member, a rigid pivoted lever shiftable by said primary member, a second rigid pivoted lever adjacent to said first lever, a. contact mounted on the free end of each lever, said contacts being adapted for engagement, a reversible electric motor, a cam driven by said motor, a crank-type driving connection between said motor and said second lever for actuating at the same angular velocity as said cam, an electrical circuit energizing said motor for rotation in a direction to eiiect engagement of said contacts and including a resistance, a directional circuit in shunt relation to the resistance of said first circuit for energizing said motor for rotation in the opposite direction, said contacts forming a switch in said directional circuit whereby said motor is energized by one or the other of said circuits at all times, and a pivoted follow-up member engaging the periphery of and actuated by said cam.

3. A follow-up apparatus comprising a primary shiftable member, a rigid pivoted lever shiftable by said primary member, a, second rigid pivoted lever adjacent to said first lever, .a, contact mounted on the free end of each lever, said contacts being adapted for engagement, a reversible electric motor, a cam driven by said motor, a rigid link pivoted at its opposite ends to said cam and said second lever, an electrical circuit continuously energizing said motor for normal rotation in a direction to effect engagement of said contacts and including a resistance, a directional circuit for energizing said motor for rotation in the opposite direction, said contacts forming a switch in said directional circuit whereby said motor is continuously energized to alternately open and close said switch, and a pivoted followup member juxtaposed to said cam, and means for urging said follow-up member against said cam.

4. A follow-up apparatus comprising a primary shiftable member having a condition-responsive element, a rigid pivoted lever shiftable by said element, a second pivoted lever adjacent to said first lever, a contact mounted on the free end of each lever, said contacts being adapted for engagement, a, reversible electric motor, a cam driven by said motor, a crank-type driving connection between said motor and said second lever, said cam and driving connection being actuated in predetermined relation by said motor, an electrical circuit energizing said motor for rotation in a direction to efiectengagement of said contacts and including a resistance, a directional circuit for changing the energization of said motor for rotation thereof in the opposite direction, said contacts forming a switch in said directional circuit to continuously operate said motor in alternate directions, and follow-up means including a shiftable member engaging and actuable by said cam.

5. A follow-up apparatus comprising a primary shiftable member including a diaphragm, a rigid contact-carrying member sliiftable in a predetermined plane response to movement of said diaphragm, a, second rigid contact-carrying member shiftable in said plane, a reversible electric motor, a cam driven by said motor, a connecting rod between said cam and said second shiftable member, an electrical circuit normally energizing said motor for rotation in a direction to close said contacts, said circuit including a resistance, a directional circuit of less resistance than said first circuit for energizing said motor for rotation in the opposite direction, said contacts forming a switch in said directional circuit to alternate the direction of motor operation continuously, and follow-up means including a shiftable member engaging the periphery of and actuated by said cam.

6. A follow-up apparatus comprising a primary device having a shiftable element, a pair of juxtaposed independent, rigid switch arms pivoted on said device, one arm being shifted by said shiftable element, a reversible power member normally urging the other arm toward the first arm, electrical means controlled by said switch for reversing said power member whereb said power member operates continuously and alternately in a hunting action to follow the movement of said shiftable element, a cam driven by said power member, and a driven member including a part shiftable in a plane perpendicular to the axis of rotation of said cam and bearing against the periphery of said cam.

FRANK DONALD BURNS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,032,016 Hitner Feb. 25, 1936 2,164,548 Smoot July 4, 1939 2,284,817 Harrison June 2, 1942 2,292,937 Harrison Aug. 11, 1942 1,458,419 Jones et a1 June 12, 1923 2,035,602 Hubbard Mar. 31, 1936 2,112,683 Wooley Mar. 29, 1938 2,344,535 Clark Mar, 21, 1944 

